Treating metals and compositions therefor



252. COMPOSITIONS,

Patented Aug. 4, 1931 UNITED STATES Examiner PATENT OFFICE JAMES C.VIGNOS, OF NITRO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICELABORATORIES COMPANY, OF AKRON, OHIO, A CORPORATION OF OEIO TREATINGMETALS AND COMPOSITIONS THEREFOR No Drawing.

The present invention relates to the cleaning and preservation ofmetallic surfaces wherein the surface is in contact with liquids of anacid nature. More particularly. the invention relates to the preventionof excessive pitting and embrittlcmeni of metals when subjected to avpickling process. The invention includes the provision of a regulator orinhibitor for causing the acid solution selectively to attack uncleanportions of metallic surfaces immersed therein to the substantialexclusion of any corrosive action upon clean portions of the metalsurface.

In the art of pickling, the metal is treated with a dilute acid toremove rust, scale or other deposits. The acid solution removes the rustand scale, but in the absence of any material preventing such action,also attacks clean portions of the metal, thereby causing pitting orother pickling of portions of the metallic surface. Such pitting isparticular- 1y detrimental and undesirable when the metal is to beplated, painted or galvanized and cold worked.

By means of the present invention the ob jectionable features of thepickling process are substantially overcome and eliminated. Toaccomplish this in accordance with the present invention, there is addedto the pickling bath or other acid solution employed, a regulating agentor ingredient which acts to restrain the action of the acid in removingthe scale or deposit. or in other words, the ingredient causes the acidselectively to re move oxides and the likewithout materially attackingthe clean portions of the metal surface.

The regulators or inhibitors which are disclosed in the presentapplication comprise organic sulphur-containing compounds of a typewherein one or moresulphur atoms are joined preferably to one or twocarbon atoms. The preferred type of compounds are organic sulfide,disulfids and .polysulfids of bothopen chain and ring structure.Compounds of the type preferred, as hereinafter set forth, compriseparticularly materials containin a grouping such as -G-S S; or -G ,-C orother groupings contain- Serial No. 246,917.

ing carbon and sulphur, such as --C=S wherein the carbon joined to thesulphur atom is linked to carbon or other atoms other than to more thanone atom of nitrogen.

The invention will be readily understood from the following descriptionand examples. In the examples set forth for carrying out the metalpickling process, conditions were imposed which duplicated, so far aspossible, those commonly followed in commercial practice, so far asconcerned acid concentrations and temperatures employed. The heating ofthe metallic test strips in the pickling liquor, in the manner ashereinafter set forth was, however, from three to four times thatordinarily followed in practice for the acid concentrations employed.Test pieces of steel approximately three inches square were cut from asheet after the annealing process had been carried out.

tion of the pickle liquor for approximately an hour while beingmaintained at a temperature of from 176 to 185 F. to C.). For this acidconcentration, commercial practice is to pickle at approximately F.(73.8 C.) for from 15 to 20 minutes. In all cases, the results werecompared with similar tests wherein the steel pieces were subjectedunder the conditions set forth to the action of an acid solution of 95the strength speclfied above, but containlng no inhibitor. Comparison ofthe loss in weight suffered by the various test pieces give at once ameasure of the inhibiting action exerted by the compounds tested.

Thus, when meroaptohenzoa-thiazolmdis ,sulfid possessing the formula wasemployed under the conditions set forth and in the proportion ofapproximately 0.01% of the weight of acid solution used, it was foundthat the loss in weight suffered by the iron was only 1/10 as great asthe loss ensuing when no inhibitor was present in the pickle bath.

In another test carried out in the manner hereinbefore described, aquantity of benzykdisnlfid, (C H .CH S equal to but 1/500 of 1% of thequantity of acid solution taken, was employed as an inhibitor. It wasfound that the presence in the acid solution of such a very smallproportion of inhibitor resulted in a pickle sheet of good appearancethat had lost less'than 1/16 as much weight as that lost by pickling inan acid solution of the same strength but containing no inhibitor.

Benzyl-disulfid when addedto the pickle liqfii'insmall prgportionsjin asolution employing furfural or phenol as a solvent gave equally goodresults both in p'ickling steel and copper sheets. Likewise the samecompounds, either alone or in conjunction with the solvents mentionedproduced an equally desirable effect when hydrochloric acid was employedin a pickle bath for treating steel and copper.

Other aromatic sulfids have also been found to exert an inhibitingaction in the pickling process. Thus -sulfid anddinitro-diphenyl-disulfid are effective in the process described.Likewise i phenyl-disulfid and,.p-p-diaminosbenzvl-di sulfid wheii iisedin the proportion 0 approximately 1/500 of 1% of the weight of acidsolution taken resulted in a saving of at least 90% of the loss thattook place when no inhibitor was present in the acid solution.

Aliphatic mono and disulfid compounds have also been found to possessdesirable characteristics as inhibitors of the action of acids uponmetal surfaces. Thus allyl-sulfid iso-amyl-mono and disulfids, ethyhdisulfid heta-heta lihydroxy-thifl saifid and other like compoms-have'allbeenfiund to exert an inhibiting action on acids emploved in a metalpickling bath. Allylsultid for example which is a typical representativeof the class of aliphatic sulfids mentioned, when employed in theroportion of approximately 1/500 of 1% of the quantity of acid solutiontaken in the process as hereinbefore described was found to diminish thequantity of dissolved metal to only about l/l0 of that resulting when noinhibitor was employed. As in the case of the other compounds mentionedthe inhibiting action of the materials is increased by the use of alarger proportion of the compounds than is set forth in the example.

Other types of sulphur-containing compounds useful in the process asherein set forth are the di.-.thioc a rb a m i c acids and theirmetallic and pgganic salts, The organic salts of such cofiiaaams' arereadily obtained by eaqting carbon bisuliid upon sec; ondaryaminesfpar'ticularly secondary aliph'zitic "amines. Thus,piperidine-penta- 'inethylen-di thiocarbamate was employed inth'e'pfo'cess'hereinbefore set forth in the proportion of 0.01 of 1% ofthe quantity of acid solution employed. The iron loss resulting fromcarrying out the pickling process in the presence of this inhibitor ofacid action was found to be approximately 7.5% of that resulting when noinhibitor was employed. In other words, the presence of such a slightproportion of this type of inhibitor resulted in a saving ofapproximately 13/14 of the loss that followed from the use of noinhibiting compound. Such a small loss per square inch of surface wouldbe practically negligible since in the example given, the loss amountedto only 0.0015 gram of each square inch of metal exposed to the acidsolution. Other..di -thiooa rb amates, containipgihq: grouping, where Xgeipresents hydrogen or an organic group, are lEWlSG effective for use'in the process described.

Ihima1 1- I11On0 and disulfids which c011- tain the groupingrespectively are also effective for preventing the excessivedeterioration of metals immersed in or subjected to the action of anacid solution. Thus, a solution was prepared for use in pickling metalscomprising 500 cc. of sulphuric acid containing approximately 8% byweight of 66 Baum acid. To this acid solution there was added Theresulting solution contained approximately 0.002% of the disulfid. Irontest strips were then immersed in the solution for about 60 minuteswhile maintaining the solution at a temperature of from 80 to 85 C. Theloss in weight of the test strips resulting from exposure to thepickling solution was observed to be only about 7.5% of the loss thatresulted when a similar test strip was pickled under the same conditionsin an acid solution containing no inhibitor. That is, the inhibitordecreased by about 13/14 the metal loss due to solvent action of theacid on the metal. This loss 252. COMPOSITIONS,

when calculated on the surface exposed to the solution amounted to but0.00155 gram per square inch of surface.

A similar test carried out in the manner as described, except thatdi-methyl-alp hanaphthyl thiuram disulfid was employed inpI'a'ceWf-the'inhibitof's'pecified in the example, yielded a resultshowing that the solvent action of the acid on the metal was decreasedby approximately 12/13. In other words, the loss in metal per squareinch of surface exposed to the acid solution was only 0.0013 gram ascompared with a loss of 0.0172 gram per square inch where no inhibitorwas employed.

A further test was completed wherein 31;;

(fiflllldii-tOlYl thiuram disulfid was employed as an inhibitofi'fi'tlie iiianner as described. An acid solution of the strengthmentioned and containing only 0.002% of the inhibitor was found to beparticularly effective for the objectdesired. Such a solution was foundto pickle iron and steel strips in such a manner that the acid loss dueto solvent action of the acid was only 3.8% as great as that takingplace when no inhibitor was employed. This loss, distributed over thearea of surface exposed to the pickle solution, amounted to only 0.00000gram per square inch as compared with a loss of 0.01722 gram per squareinch when no inhibitor was employed.

Other thiuramsulfids have also been found to possess adesirableTnhibiting effect when employed in quantities comprising lessthan 1% of the pickle solution. Tests similar to those hereinbefore setforth have been carried out wherein di=ethyl-.d i- )lien l thim:am iilllfidsfilllyl.ill llli BIQE OHIMUEQQY .tl1iuram di sulfid and the lilfewere employed as inhibitors and found to retard the action of acid upona metal.

By proceeding in a like manner, similar beneficial effects wereascertained to be exercised when thiuram disulfids were employed in apickle liquor comprising hydrochloric acid. Other metals, such as copperand the like were also protected from undue corrosion by acids when thepreferred type of inhibitors were employed in the pickling liquor. It isevident from the various examples hereinbefore set forth, that organicsulfids, disulfids, and polysulfids comprise a class of effectiveinhibitors in processes wherein metals are subjected to the action of anacid. Greater inhibiting action has been found to be produced by the useof a larger quantity of the various compounds than that set forth in theexamples. It is not, however, necessary to employ an acid solutioncontaining more than 1% by weight of the inhibiting compound, nor is itdesirable to use a greater quantity than will completely dissolve in thesolution employed.

The examples hereinbefore set forth are Examiner to be understood asillustrative only and not at all limitative of the scope of theinvention. Other examples of the process described are apparent to thoseskilled in the art to which the invention pertains wherein differentacid concentrations, times of treatment and temperatures may beemployed. The invention is to be considered as limited solely by thefollowing claims wherein the invention is claimed as broadly as ispossible in view of the prior art.

What is claimed is:

1. A process of pickling iron and steel products which comprisessubjecting the metal to be pickled to the action of a sulfuric acidsolution containing a small proportion of an aromatic disulfid compound.

2. A process of pickling iron and steel products which comprisessubjecting the metal to be pickled to the action of a sulfuric acidsolution containing a small proportion of benzyl-disulfid.

3. A pickling bath for iron and steel products comprising sulphuric acidcontaining more than 0.01% but less than 1% by weight of an organicdisulfid compound free of amino substituents.

4. A pickling bath for iron and steel products comprising sulphuric acidcontaining more than 0.01% but less than 1% by weight of an aromaticdisulfid compound.

5. A pickling bath for iron and steel products comprising sulphuric acidcontaining more than 0.01% but less than 1% by weight ofbenzyl-disulfid.

6. A metal treating compound comprising a sulfuric acid solution of anaromatic disulfid.

7. A metal treating compound comprising a sulphuric acid solution ofbenzyldisulfid.

8. A pickling bath for metals containing an aryl disulfid compound;

9. A pickling bath for metal containing benzyl disulfid.

In testimony whereof I hereunto afiix my signature.

JAMES C. VIGNOS.

